I would install the beta in a separate partition. I don’t think is safe to install it on your main OS. To create a partition go to Disk Utility, I created one with 25 GBs and it worked perfectly. If you still decide to install it as your primary OS, don’t hesitate to backup. You may lose your data as Yosemite is a beta.
If you don’t need to use any special software I think an iPad will fulfill any student’s needs. The regular sized iPad will be ideal for the screen size.